From the transcript of the NPR interview between David Greene and former NSA official Richard Clarke:

CLARKE: … If I were in the job now, I would have simply told the FBI to call Fort Meade, the headquarters of the National Security Agency, and NSA would have solved this problem for them. They're not as interested in solving the problem as they are in getting a legal precedent.

GREENE: Wow, that sounds like quite a charge. You're suggesting they could have just gone to the NSA to crack this iPhone but they're presenting this case because they want to set a precedent to be able to do it in the future?

CLARKE: Every expert I know believes that NSA could crack this phone. They want the precedent that the government can compel a computer device manufacturer to allow the government in.

As suspected, there is probably a physical way around iPhone security features. One of the truisms in computer security is: if someone has physical access to the device, there is virtually no security that cannot be bypassed.